🔍 Key Concepts

• Direct Digital Synthesizer (DDS) output spectrum structure • Difference between broadband noise and discrete spectral lines • Effect of phase accumulator and lookup table quantization in DDS

💭 Think About

• When a DDS generates a sine wave using a phase accumulator and lookup table, what kind of spectral artifacts does phase truncation and finite word length create: continuous noise or isolated frequency lines? • Which choice describes energy spread smoothly over a wide range of frequencies, and which describes tones at specific frequency offsets from the carrier? • Think about a spectrum analyzer view of a DDS output: do you mainly see a raised noise floor everywhere, or specific narrow unwanted tones around the main signal?

✅ Before You Answer

• Clearly distinguish between broadband noise (spread over many frequencies) and spurious tones (narrow, at specific frequencies). • Recall that quantization and truncation in DDS typically produce repeatable, deterministic artifacts rather than purely random noise. • Ask: On a plotted DDS spectrum, what unwanted features are usually specified in terms of spurious-free dynamic range (SFDR)? That points to the key type of unwanted component.